Multicomponent fibers are, in and of themselves, well known and have been used extensively to achieve various fiber properties. For example, multicomponent fibers have been formed of two dissimilar polymers so as to impart self-crimping properties. See U.S. Pat. No. 3,718,534 to Okamoto et al. and U.S. Pat. No. 4,439,487 to Jennings. Multicomponent fibers of two materials having disparate melting points for forming point bonded nonwovens are known, for example, from U.S. Pat. No. 4,732,809 to Harris et al. Asymmetric nylon-nylon sheath-core multicomponent fibers are known from U.S. Pat. No. 4,069,363 to Seagraves et al.
One problem that is encountered when multicomponent fibers are formed having distinct domains of dissimilar polymers which are incompatible with one another is that the domains often separate at the boundary between the domains. This separation results in fracturing or splitting of the fiber thereby weakening the system (e.g., yarn, fabric, carpet or like textile product) in which the fiber is used. Weakening of the fiber system can be sufficiently acute to prevent the system from undergoing downstream processing (e.g., drawing, texturing, heat-setting, tufting, knitting, weaving and the like). Furthermore, such fracturing and/or splitting of the fibers can result in poor product qualities such as poor appearance and poor wear performance.
It would therefore be highly desirable if multicomponent fibers having distinct longitudinally coextensive polymer domains formed of different polymers could be produced which have minimal (if any) inter-domain fracturing and/or splitting. It is towards providing such a fiber and method of producing the same that the present invention is directed.
Broadly, the present invention is directed to a multicomponent fiber and methods and apparatus of producing the same whereby an inter-domain boundary layer is interposed between distinct domains formed of different polymers so as to minimize (if not eliminate entirely) separation of the domains at their interfacial boundary. The inter-domain boundary layer therefore is provided so as to provide an interlocking region between the fiber domains and thereby impart greater structural integrity to the fiber.
In preferred embodiments, the inter-boundary layer is formed of a heterogeneous mixture of the polymers forming the respective distinct fiber domains. That is, the interboundary layer will include rivulets or fingers of each polymer forming the adjacent domains which interlock with one another in a randomly tortuous manner. These different polymer rivulets thereby effectively increase the surface area at the interfacial boundary between the fiber domains thereby increasing the adhesion therebetween. In addition, a certain degree of mechanical interlocking is believed to occur by virtue of the randomly tortuous manner in which such rivulets are physically disposed in the inter-domain layer.
These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiments thereof which follow.